1. Field of the Invention
This invention relates to protecting organic-matrix based composite materials from damage by fire and consequent release of noxious gases and smoke. It especially relates to adding an inorganic surface coating that delays the heat-up rate and reduces the overall temperature on the back side of a composite structure.
2. Review of the Prior Art
Aerospace use of composites relies heavily on epoxy resins for providing optimum mechanical properties at much reduced weight. Marine applications of composites have continued to depend on polyester matrices as dictated by size, cost, and the ability to tailor-cure parameters, particularly gel times and exotherm rates. As requirements for reduced weight, better fire and smoke properties, and mechanical properties increase for a number of potential ship applications,(such as masts, sonar domes, deckhouses, and minesweeper hulls), new or modified resins are needed that exhibit superior properties over those currently used.
Composite structures are potentially very useful for improving specific structural characteristics of Naval ships and submarines while reducing weight, but the combustible nature of the polymeric components of such structures has limited the usage of these materials because the conventional polyester and epoxy types currently used in shipboard applications and the epoxy types used in aerospace applications will support combustion and evolve large quantities of smoke while burning.
The minimum thickness of a suitable composite structure for such applications is 1/8 inch. Addition of a thin thermal barrier that could block incoming radiation, so that heating must occur primarily by conduction rather than radiation, could delay the heat-up rate and reduce the overall temperature on the back side of the structure, thereby increasing fire resistance and reducing evolution of smoke and noxious gases.
Because of high temperatures and impact velocity, however, ceramic coatings cannot be sprayed directly onto engineering plastics without substrate degradation, such as warping of the plastic structure, charring and/or melting of its surface, or peeling of the coating.
A commercial aircraft application has demonstrated a ceramic/graphite hybrid composite firewall which, when installed in a Lear Fan 2100 aircraft, must contain a 2000.degree. F. fire and provide 15 minutes of protection to airframe components, as described by Fell et al in "The First All Composite Firewall as Developed and Designed for the Lear Fan 2100", 28th National SAMPE Symposium, Apr. 12-14, 1983.
U.S. Pat. No. 4,460,529 discloses a quasi-isothermal process for manufacturing ceramic or ceramic oxide hollow bodies without use of a binder, an adhering substrate, or internal embedded supports by spraying hot atomized ceramic or ceramic oxide particles as a plasma onto a non-adhering, highly thermally conductive, internally cooled mold core which is mounted on a rotating lathe which in turn is mounted on a longitudinally movable carriage. After removal from the mold core, the hollow body is capable of being directly used without sintering.